1. Field of the Invention
The present invention relates to a board-to-board test unit for testing the consistency of subscriber data and cabling (allocation of a time slot) while bridging a new and an old switches prior to replacement of an old switch with a new switch so that the replacement can be instantaneously completed without disturbing services to the subscriber.
2. Description of the Related Art
With the development of advanced switches in the telephone switching network, etc., an old switch often has to be replaced with a new switch.
In this case, however, the replacement must be conducted instantaneously without disturbing services to subscribers accommodated in the old switch. Therefore, a test must be conducted with the old switch operated in the normal operating condition when the consistency test of the new switch on subscriber data and time slot allocation is conducted prior to the replacement.
The test described above is commonly called "a board-to-board test" because a board-to-board test loop is configured through both the old and new switches. FIG. 1 shows an example of a board-to-board test of the prior art technology.
Prior to the replacement, an analog subscriber line 102 assigned to an analog subscriber 101 (telephone, facsimile, etc.) is accommodated in a subscriber card (subscriber circuit) 104 of an old switch 105 through a main distribution frame (MDF) 103. The following board-to-board test is conducted before the replacement of the old switch 105 with a new switch 106 is performed in the above described way.
In the MDF103, in addition to the connection between the analog subscriber line 102 (shown in broken line A in FIG. 1) and the old switch 105, a bridge (shown in broken line B) is provided between the analog subscriber line 102 and a subscriber card 107, which is assigned for the subscriber line 102, of the new switch 106.
Next, a board-to-board test unit (BTBTU) 108 is connected to standard no-test trunks (NTT) 109 and 110 each connected to the old switch 105 and the new switch 106 respectively. The both old and new switches have a basic capability to provide a metallic access pass from the BTBTU 108 to the subscriber line 102 through respective subscriber cards 104 and 107, metallic test access lines 111 and 112, and the NTTs 109 and 110.
The BTBTU108 has a data base of the analog subscriber's phone number whose line is to be tested, and sends the same subscriber number to both an old and new switches 105 and 106 (refer to SIG1 in FIG. 1).
If both the subscriber database of the new switch 106 is correct, and if the subscriber line 102 is correctly wired to the new switch 106 through the MDF 103, a metallic line loop is formed successfully from the BTBTU108 to the new switch 106 through the old switch 105 and the MDF 103 (refer to SIG2 in FIG. 1).
Then, the BTBTU108 sends a communication signal from the old switch 105 as one end of the loop, compares it with the communication signal turned around from the new switch 106 as the other end of the loop, thus performing a consistency test of the above described bridge.
Recently, digital subscriber line is used to secure the quality of voice communication and reduce the installation cost of subscriber line in such a case where a central office terminal is located apart from a subscriber.
That is, as shown in FIG. 2, a remote subscriber 201 is accommodated in a remote terminal (RT) 203 which forms a part of a digital loop carrier (DLC) through a subscriber line circuit (SLC) 202.
Communication signals and call control signals are transmitted between switches and the RT203 through standard PCM transmission facilities. If a switch is an analog type switch 208 as shown in FIG. 2, digitally multiplexed subscriber signals (referred to as a digital subscriber) is re-converted to an analog voice frequency signal (VF) by a central office terminal (COT), through digital cross connect (DSX) 205, located in the site where the analog switch 208 is located. Then, the re-converted analog voice signal VF is treated by the analog switch 208 as if the remote analog subscriber 202 is locally accommodated.
Thus, the digital loop carrier (DLC) for accommodating a digital subscriber in the analog switch through a COT as described above is referred to as "universal digital loop carrier (UDLC)."
On the other hand, recently, the digital switch has become more popular, replacing the conventional analog switch with a view to improving communication services. FIG. 3 shows an example of a configuration where the digital subscriber is accommodated in the digital switch.
A digital switch 301 handles voice data to/from the digital subscriber as the digital signal through a digital terminal (DT) 302. Thus, the DLC for accommodating a digital subscriber directly in the digital switch through the DT is referred to as "integrated digital loop carrier (IDLC)."
In the UDLC shown in FIG. 2, if the board-to-board test is conducted at the replacement of the analog switch with another analog switch, it is recommended that a metallic line path is formed in a COT206 (on the side of the switch) as shown in FIG. 1, and a physical loop should be formed by providing with a bridge in an MDF between two switches as shown in FIG. 1.
However, recently in most cases, a conventional analog switch is replaced with a new type digital switch. Therefore, the UDLC is converted, and accommodated in a new digital switch as an IDLC. In such cases, after the completion of replacement, the appearances of digital subscribers are in the time slots multiplexed on a PCM line, thus prohibiting the formation of a physical loop shown in FIG. 1. Therefore, in a board-to-board test described above, it should be determined whether or not a subscriber to be tested is logically allocated to a corresponding time slot in the PCM line in the correct way.
Therefore, in such a case, the conventional board-to-board test is not applicable, causing a problem that mis-engineering or mis-connection are often overlooked.